PAM-Pellet additive manufacturing technology is an additive manufacturing process based on the principle of material extrusion granulate. Injection molding feedstocks made of a thermoplastic polymer (which may contain a ceramic or metallic filler) are melted in a screw system and conveyed through a nozzle to form material strands. Like for filament extrusion systems, the objects are made up of a set of superimposed layers produced by the juxtaposition of individual strands. The technology has the advantage of exploiting commercial CIM or MIM feedstocks, which makes it very advantageous in terms of operating cost.

In the present work, we evaluate the suitability of this technology to produce dense ceramic parts. Zirconia commercial ceramic feedstocks (INMAFLOW K2015 – INMATEC Gmbh Germany) were implemented on a PAM-MC equipment (Pollen AM – France).
After qualification of the injection granules (SEM observations) and determination of the debinding conditions (under acetone followed by thermo-gravimetric analysis under air), a parametric study allowed to determine the optimal printing conditions. Based on a qualitative examination of the test pieces (absence of over/under extrusion and/or macroscopic defects) as well as optical microscopy observations (absence of detectable porosities), specimens were printed and debinded. The influence of the nozzle geometry was shown to be critical for both the quality and the reliability of the printing. After sintering, maximum densities of up to 99.3% of the theoretical density could be obtained, values comparable to the supplier's data sheet for injected parts. The hardness of polished samples was measured around 1350 Vickers and an average 3-point bending strength of 974 MPa was experimentally determined. The fact that these values are quite excellent as well as the ease of implementation of the PAM technology make it a credible technology for the production of technical ceramics.
Nevertheless, an inherent limitation of additive extrusion processes such as PAM is the surface finish. Sintered parts retain a "staircase" appearance resulting from the overlapping beads. The reduction of the printing nozzle section allows to gain in resolution but this is done at the expense of printing time and reliability. In this work, we demonstrate the possibility of hybridizing PAM printing adding a finishing operation by milling in the green state. This manufacturing chain significantly improves the surface quality and allows a dramatic reduction of the cycle time thanks to the use of coarse printing nozzles (1 mm). An example is given for the manufacture of a watch case.